Multicarrier transmission is becoming a focus of attention as a high-speed transmission technique that reduces the influence of frequency selective fading caused by multipath channels. In this multicarrier transmission, sharp power peaks are produced in a generated multicarrier signal. When these signals having great peaks are inputted to a nonlinear amplifier, these signals are amplified in a nonlinear amplifier with nonlinear distortion, and so, these are causes of deterioration of transmission characteristics and out-of-band radiation in multicarrier transmission. To prevent this, it is conceivable that back-off may be provided with a nonlinear amplifier, but, efficiency of an amplifier deteriorates.
Then, various techniques (e.g. Patent documents 1 and 2) to reduce peaks in multicarrier signals, are proposed.
For example, in Patent Document 2, peak reduction is attempted as the following steps. That is, first, peaks for transmission data are detected using a threshold, and differential data between the peaks and the threshold, that is, peak components that are beyond a threshold in a signal, are generated. Second, the generated peak components are band-limited by filter processing. Third, peak components after band-limiting are subtracted from the original transmission data. As such, transmission data where peaks are decreased is formed.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-185432    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-104162